This invention relates to a method of controlling a motor vehicle during speed change operations and an apparatus for performing this control and, more particularly, to engine torque control for avoiding gearshift shock when the speed of a stepping-type transmission is changed.
A method in which the torque output from an engine of a vehicle with an automatic stepping transmission placed at and connected to the rear end thereof is reduced during a gearshift operation in order to avoid gearshift shock is known (hereinafter referred to as engine torque control). Examples of this method are disclosed in U.S. Pat. No. 4,266,447 [German Pat. No. 2848624, European Pat No. 11088, Japanese Patent Laid-Open No. 55(1980)-69738].
These examples of the conventional control method make use of a particular type of system for reducing the output torque during gearshift in which the engine revolutions is detected when the need for a gearshift operation is determined; values representing the engine revolutions at which the engine torque control should be started and terminated are set by calculation of such parameters as the gear ratios before and after the selected gearshift operation; and the engine torque control is started and terminated when the engine speeds actually reach the set values. It is preferable that the timing of the start or end of the engine torque control to be made to coincide with the timing of the start or end of the gearshift operation, and the system is designed to predict and set the requisite values for effecting this coincidence.
It is possible that this conventional method may be effective in terms of a reduction in the magnitude of gearshift shock as originally intended under certain limited conditions. In general, however, this method experiences the following problems:
(1) It is difficult to control a gearshift operation with consistent accuracy under the influence of variations in the vehicle speed and the state of acceleration after the setting of the engine revolutions at which the engine is assumed to rotate at the start and end of the gearshift operation. Such influence cannot be avoided so long as the method is based on this prediction-based control.
(2) The engine revolutions is a substitute characteristic in terms of the detection of a transient state brought about by a gearshift operation, and engine revolutions involves slipping rotation of the torque converter. Control based on this factor is defective in terms of detection of such a transient state, as well as in terms of the response characteristics if it is effected with respect to a range of operation in which changes in the engine revolutions are gradual and small, in particular when operating with a small load and a low vehicle speed. It is therefore difficult to achieve engine torque control with a high degree of accuracy.